1. Field of the Invention
The present invention relates to an improved check valve suitable for general purpose use or for use on instrument lines or valve operating accessories where the pressures encountered are very low (inches of water column) to very high (several thousand psi).
2. Related Art
Currently known check valves for low differential pressure application (low cracking pressure) are either not reliable after a few cycles of operation or the cracking pressure is too high for operating in the inches of water column pressure range.
Common check valves utilize a light force spring and a soft elastomeric seal to close the valve against backflow. Another method is to utilize a ball or piston as the moving/sealing member, with or without the aid of a spring.
Another method of construction is to use a member that is hinged on one edge (usually the top edge) which allows the member to swing closed or open depending on the pressure conditions in the valve. This type of construction is usually reserved for larger size valves.
A disadvantage of common check valves is that the elastomeric sealing material must be carefully selected for chemical compatibility with the service medium.
The Anderson-Greenwood diaphragm-type check valve (U.S. Pat. No. 3,534,768) was designed to overcome the relatively high inertia required to open instrument check valves available at that time. The design is plausible but after just a few cycles of operation, the teflon diaphragm takes a "set" (or loss of "memory") which renders the check valve incapable of stopping flow or leakage when the pressure condition is reversed.
It is an advantage of the present check valve that it is capable of withstanding high system pressure while allowing the seat to "crack" open or seal with just an inch or two of water column pressure. It is a simple three-piece design readily made from materials of construction that are compatible with most chemicals.